1. Field of the Invention
The present invention relates to a hub unit bearing apparatus for rotatably supporting driving wheels of a motor vehicle (front wheels of an FF car, rear wheels of an FR car, front and rear wheels of a 4 WD car).
2. Related Background Art
In the past, in order to rotatably support driving wheels of a motor vehicle, various kinds of hub unit bearing apparatuses have been used (for example, refer to the Japanese Patent Laid-Open Nos. 63-246677 and 64-28056). An example of them is shown in FIG. 3.
In FIG. 3, a shaft 51 of a constant velocity joint 84 comprises a first inner toward the center of the vehicle, i.e., right side in FIG. 3) enlarged diameter portion 52, a first outer reduced diameter portion 53, and a first stepped portion 54 connecting these diameter portions. A male threaded portion 55 (shown diagrammatically) is formed on an outer peripheral surface of an outer end of the first reduced diameter portion 53 and a male spline groove portion 56 is formed on the peripheral surface of the remaining portion of the first reduced diameter portion 53.
A first flange 60 for supporting a wheel 58 constituting a vehicle wheel and a disc rotor 59 constituting part of a braking system is formed on an outer peripheral surface of a cylindrical hub 57 fitted on the shaft 51. Further, a female spline groove portion 61 capable of engaging the spline groove portion 56 is formed on an inner peripheral surface of the hub 57. A first inner race track 63 is directly formed on an outer peripheral surface of a second enlarged diameter portion 62 at an intermediate area of the hub 57. Further, an inner race 65 is fitted on a peripheral surface of a second reduced diameter portion 64 near an inner end of the hub 57, and a second inner race track 66 is formed on an outer peripheral surface of the inner race.
An inner end face (right end face in FIG. 3) of the inner race 65 is protruded inwardly more than an inner end face of the hub 57 and is abutted against the first stepped portion 54. Accordingly, the inner race 65 is sandwiched between the first stepped portion 54, and a second stepped portion 67 connecting the second enlarged diameter portion 62 to the second reduced diameter portion 64.
The male threaded portion 55 formed on the peripheral surface of the outer end of the shaft 51 of the constant velocity joint 84 is protruded outwardly from an outer end face of the hub 57, and a nut 68 is screwed on the protruded end of the threaded portion. As a result, the inner race 65, the hub 57 and a washer 69 are sandwiched between an inner end face of the nut 68 and the first stepped portion 54.
A cylindrical outer race 76 is disposed around the hub 57. A pair of outer race tracks 70 are formed in an inner peripheral surface of the outer race 76 in confronting relation to the above-mentioned first and second inner race tracks 63, 66, and a plurality of rolling members 71 are disposed between the respective inner and outer race tracks. A second flange 72 for mounting the outer race 76 onto a suspension system is formed on an outer peripheral surface of the outer race 76. Incidentally, the reference numeral 73 denotes a sensor rotor fitted on a portion of the shaft 51 of the constant velocity joint 84, and 74 denotes a rotational speed detecting sensor supported by an arm 75 of the suspension system of the vehicle body.
In the hub unit bearing apparatus having the above-mentioned construction, the rotation of the rolling members 71 permits the rotation of the hub 57, inner race 65 and shaft 51 inside the outer race 76. Further, the rotational speed of the hub 57 is detected by the rotational speed detecting sensor 74.
Also in the above-mentioned hub unit bearing apparatus, by using the single nut 68, not only the hub 57 is fixedly supported by the shaft 51 of the constant velocity joint 84, but also the inner race 65 is fixed to the hub 57. Thus, if the nut 68 is loosened, the inner race 65 is moved with respect to the hub 57, with the result that the hub 57 cannot be rotated smoothly. To avoid this, if the tightening torque for the nut 68 is increased to prevent the looseness of the nut, the pre-load acting on the bearing will be increased, thus shortening the service life of the rolling bearing assembled to rotatably support the hub 57 within the outer race 76.
For these reasons, in the past, the nut 68 was prevented from loosing and the pre-load of the bearing was adjusted by strict control of the tightening torque for the nut 58 during the assembling of the rotary members of the vehicle wheels. Thus, the assembling of the rotary members in the vehicle production line became troublesome.